Earth’s climate has changed naturally throughout history, long before human influence. Evidence of these past changes is preserved in natural archives like tree rings, glacial ice layers, ocean sediments, coral reefs, and sedimentary rocks. For instance, air bubbles trapped within glacial ice provide samples of Earth’s ancient atmosphere, allowing scientists to analyze greenhouse gas levels stretching back 800,000 years. The ice’s chemical composition also reveals past global temperatures.
For a deeper dive, explore the Earth Observatory’s Paleoclimatology series to understand how scientists investigate Earth’s climate history.
This graph illustrates temperature variations over hundreds of thousands of years, derived from Antarctic ice core data, highlighting the cyclical nature of ice ages and warmer interglacial periods in Earth’s past climate record.
Scientists use this historical evidence to reconstruct “paleoclimates,” building a long-term record of Earth’s climate patterns. By combining paleoclimate data with sophisticated global climate models, they’ve identified past ice ages and periods that were even warmer than today. However, the paleoclimate record also makes it clear: the current global warming trend is happening at an unprecedented rate compared to historical warming events.
Coming out of past ice ages over the last million years, global temperatures increased by 4 to 7 degrees Celsius over approximately 5,000 years. In stark contrast, the last century alone has seen a temperature increase of about 0.7 degrees Celsius. This signifies that the current warming rate is roughly ten times faster than the average warming rate observed during the recovery from ice ages. This rapid change is what makes today’s temperature trends so concerning.
This graph compares historical temperature reconstructions from paleoclimate data with temperature records from modern instruments, showing a significant and accelerated warming trend in recent times, exceeding natural historical fluctuations.
Climate models predict a further Earth warming of 2 to 6 degrees Celsius within the next century. Historically, when global warming of about 5 degrees Celsius has occurred naturally over the past two million years, it has taken the planet around 5,000 years to reach that level. The projected warming rate for the coming century is at least 20 times faster. This accelerated pace of temperature change is what makes current global warming distinctly unusual and a cause for concern when we consider “What Is The Temperature Today” in a broader context. The speed of change, not just the temperature itself, is the critical difference.
